N. V. Lyalina

Electrochemical behavior of Co3C carbide

The electrochemical properties of the Co3C carbide have been studied. In contrast to metallic cobalt, its carbide is characterized by higher electrocatalytic activity in the hydrogen evolution reaction and low rate of anodic oxidation in acidic sulfate solutions. The oxidation in borate solutions (pH = 6.3–9.0) results in the formation of oxide films different in phase composition. In the case of metallic cobalt, a passive film consisting of CoO and Co(OH)2 forms, while the cobalt carbide oxidation results in the formation of the Co3O4 film. The oxidation of cobalt carbide is an irreversible process accompanied by the accumulation of carbon on the surface.

Corrosion-electrochemical properties of α-Fe + Fe3C + TiC nanocomposites in neutral environments

The corrosion-electrochemical properties of α-Fe + Fe3C + TiC three-phase nanocrystalline composites in borate solutions with pH 6.3–9.0 both with and without NaCl are studied. α-Fe + Fe3C + TiC composites are found to have heightened resistances at active-oxidation potentials of α-Fe and cementite due to the formation of xFeO · yTiO2 mixed surface oxides. The protective properties of passive films based on xFeO · yTiO2 and their resistance to local activation are worse than those of Fe3O4/γ-Fe2O3 (γ-FeOOH) passive films formed on iron and α-Fe + Fe3C composites.

The electrochemical properties of Ni3C carbide

The electrochemical properties of Ni3C was studied. In acidic sulfate solutions, the carbide is characterized by high overpotential of its oxidation as compared with nickel. In the case of carbide oxidation, the anodic reaction orders with respect to anions are low, indicating a weak dependence of the rate of the anodic process on the solution composition. Significant differences in the kinetics of the anodic processes indicate different mechanisms of the oxidation of nickel and its carbide. The rate and kinetic parameters of the hydrogen evolution reaction are comparable on Ni and Ni3C. In neutral and alkaline solutions, the metal and carbide samples were similar in their electrochemical characteristics. The anodically grown oxide film is thinner on nickel carbide than on nickel metal, and the oxide formed on the carbide is more readily reduced under cathodic polarization. This film is also more resistant to the pitting attack than the oxide film on nickel metal.

Effect of ambient humidity to wetting angles of various hydrophilic surfaces

The effect of ambient humidity to water and dimethyl sulfoxide wetting angles of paraffin and polyethylene terephthalate surfaces was studied. Symbasis of this relationship was found for hydrophilic polyethylene terephthalate film surface, evidencing apparently lower polarity of polyethylene terephthalate surface at higher ambient humidity. An opposite relationship of wetting angles vs. ambient humidity was observed for paraffin/water system. No relationship of wetting angles vs. ambient humidity was detected for paraffin/dimethyl sulfoxide system.

The influence of the ultrafine-grained structure on passivation of copper

The influence of ultrafine-grained structure on passivation of copper in borate solutions was studied. Ultrafine-grained cooper was prepared by the equal channel angular extrusion. It was shown that, under the conditions of anodic oxidation, an oxide film with improved protective properties is formed on the ultrafine-grained sample. This film is characterized by a small thickness, low roughness, and high content of copper(I) oxide.

Cathodic evolution of hydrogen on carbides of iron-family metals

The activity of carbides of iron-family metals with respect to hydrogen evolution in acidic solutions is found to be much higher than the activity of the corresponding metals and increase in the sequence Ni3C < Co3C < Fe3C. Of the carbides studied, cementite has the highest activity, which is comparable to that of a Pt electrode.

Passivation and local activation of α-Fe + MeC + Fe3C (Me = Ti, V, or Nb) nanocrystalline composites in neutral environments

The electrochemical behavior of α-Fe + MeC + Fe3C (Me = Ti, V, or Nb) nanocrystalline carbide-steel analogs, which were produced by mechanical activation in an organic environment followed by compaction, is studied. Passivation of the composites in borate solutions is found to be determined by the formation of FeO · xTiO2, FeO · xNb2O5, and FeO · xV2O3 (FeO · xVO2) mixed oxides, which substantially increase the resistance against oxidation at potentials of the active dissolution of ferrite phase. Resistance against local activation increases with an increase in the content of MeC and Fe3C carbide phases.

Corrosion-electrochemical properties of nanocomposites of α-Fe+Fe3C+VC in acidic and alkaline sulfate solutions

This work studies corrosion-electrochemical properties of three-phase composites of α-Fe+ Fe3C + VC in acidic and alkaline sulfate solutions. Nanosize carbide inclusions are characterized by a high level of activity in the reaction of cathodic hydrogen evolution and result in a high rate of composite dissolution in acidic solutions. The presence of carbides and carbon has a negative effect on passivation of the iron matrix. The resistance of vanadium carbide inclusions to anodic oxidation increases upon a decrease in the amount of carbon in the carbide.

Corrosion-electrochemical properties of α-Fe + Fe3C + TiC nanocomposites in acidic sulfate solutions

Corrosion-electrochemical properties of model α-Fe + Fe3C + TiC three-phase nanocrystalline composites in acidic sulfate solutions are studied. Anodic processes on α-Fe + Fe3C + TiC composites are determined chiefly by the oxidation of ferrite and cementite components. The passivation of nanocomposites takes place due to the formation of γ-Fe2O3 · nH2O surface hydroxides with a high water content n = 0.7–2.2 and low protective properties. The high activity of α-Fe + Fe3C + TiC composites with respect to hydrogen evolution is determined by the cementite component and increases with an increase in the dispersion of Fe3C inclusions. Under the effect of cathodic hydrogen, titanium carbide decomposes to produce free carbon.

Effect of sodium dodecyl sulfate and carbon particles/nanotubes on electrodeposition of polyaniline from oxalic acid solution

The effect of sodium dodecyl sulfate and carbon particles/nanotubes on the electropolymerization of aniline from oxalic acid solution onto a graphite electrode was investigated. The morphology and chemical structure of the as-synthesized polyaniline films were studied by means of SEM, XPS, NEXAFS, FTIR, and Raman spectroscopy. The electrochemical characteristics of the films were also analyzed in sulfuric acid solution. It has been shown that in the presence of sodium dodecyl sulfate, the polymerization rate increases significantly. In the synthesized polyaniline films, all imine groups and most of amine groups are protonated, with dodecyl sulfate ions being intercalated in the polymer. In the presence of sodium dodecyl sulfate, plate-like polyaniline forms large agglomerates with an extended surface and high electrochemical activity. It has been shown that the electrodeposition carried out in the presence of sodium dodecyl sulfate and suspended activated graphite particles or carbon nanotubes favors the formation of composite coatings with high specific capacitance.